Launching of Unmanned Aerial Vehicles (UAVs) can be achieved by pneumatic or rubber catapult means, where the launcher accelerates the UAV to flight speeds in a short time through air propulsion or the elastic energy stored in the rubber. Recovery systems of UAVs without runways typically employ parachute or airbag, where the UAV deploys the parachute or airbag to reduce the forward thrust force of the UAV and it subsequently lands in an open area. Alternatively, net-based recovery systems are widely used as well. U.S. Pat. No. 4,753,400 discloses such a net-based recovery system which captures the UAV during flight. In this system, a recovery net is attached to a parachute and coupled together with a tow line and are held together by a winch on the deck of the ship. During operation, the parachute glides the net to the desired altitude and the UAV flies towards the net and is captured. Thereafter, the recovery net and the trapped UAV are winched back onto the ship.
The presence of cross winds is not ideal to launch UAVs as they are light and winds may dislodge a UAV from its intended flight path. Therefore, large open areas are required for pneumatic or rubber catapults to launch UAVs against the unpredictable wind direction. Having a large open area is usually not possible when the launch is on a ship or in a forest. Pneumatic or rubber catapult launch methods also require a substantial amount of logistic resources because of their design and bulkiness. Although a runway is not needed for airbag or parachute deployment or recovery, a large open area (about 50 to 100 meters in diameter depending on size of UAV) is required for UAV landing due to poor landing accuracy of such a design. Similarly, there is a lack of adequate space for this method of recovery when operations are in a forest or on a ship. Even though net-based recovery systems need less space, they require precision control and are also labour intensive. In addition, the UAV approaches the net at high speed during recovery and may endanger the ship's structure and the people near the net. The impact caused by the sudden stoppage of the UAV in flight may damage the UAV as well.
An alternative launch and recovery system using a parasail is disclosed in US2005/0017129 A1. In this prior art launch system, the UAV is attached to a parasail which is tied to a towline and a winch on the ship. The parasail is then inflated and raised into the air. The winch reels out the parasail to a sufficient altitude and the UAV subsequently detaches from the parasail and free falls. The UAV will then achieve sufficient airspeed during the dive for the pilot to comfortably control it. One drawback of this system is that the parasail is disadvantageously behind the ship and the UAV may strike the ship and the towline of the parasail after detachment. Furthermore, air turbulence behind the ship's structure may cause the UAV to deviate from its intended flight path.
The recovery system of US2005/0017129 A1 uses an arrestor line held up by a lifting apparatus on a ship to capture the UAV using latching mechanisms on the UAV. This aerial recovery method induces great impact forces on the UAV as it is flying at high speeds. High energy loads on the UAV due to the abrupt stoppage may damage the UAV during recovery. This recovery system also requires precision control of the UAV to engage the latching mechanism onto the arrestor line. Furthermore, retrofitting a lifting apparatus onto a ship amounts to huge costs and logistical work.
As a consequence, there is a need for a UAV launch and recovery system that seeks to address at least some of the above problems or provide a useful alternative.